Bug fix#17149 User Validation on Audit Repository .Save Method

[IbrahimMNada]

Description

If there's an existing issue for this PR then this fixes https://github.com/umbraco/Umbraco-CMS/issues/17149

this pull request is a fix for this issue : https://github.com/umbraco/Umbraco-CMS/issues/17149

Which states that a content publish can be established using ContentService with a non existing user.

A Simple Database Validation/ and simple caching mechanism were added in order to check if the user really exists in the database